1. Technical Field
The invention relates in general to solenoid control elements for hydraulic valves and more particularly to a quick fitting replacement solenoid for use as a diagnostic tool or backup actuator for a spool type hydraulic valve in a closed hydraulic circuit.
2. Description of the Problem
Vehicle mounted hydraulic systems have been employed for diverse purposes including positioning snowplows, compacting trash, moving support beds and other functions. Such hydraulic systems are controlled using spool valves and these spool valves in turn have often been manually activated, with handles mechanically linked to the spool valves. The mechanical link must of course be sealed to avoid spillage of pressurized hydraulic fluid. However, these seals are prone to wear and leaks almost invariably develop.
To avoid, or at least postpone, the development of leaks, solenoid controlled hydraulic valves have been developed. A solenoid coil is used to generate magnetic fields to control positioning of the spool valve inside the valve body without the need for a mechanical linkage through the valve body. Without a mechanical linkage, the need for mechanical seals around a linkage is eliminated. Solenoid actuated valves are much less prone to leakage than mechanically actuated valves, but they complicate making provision for fitting an override control mechanism to the valve. Some manufacturer's have retained a mechanical linkage to use as a backup to the electromagnetic system. While the linkages are now used less often, they still represent a compromise of the full sealing of the hydraulic system, and they can still develop leaks over time due to thermal cycling or chemical attack. The use of solenoids also eases integration between a vehicle's hydraulic systems and the vehicle's electronic control systems. This in turn raises questions in some minds as to the reliability of the electronic controls or the ability to diagnose a problem as being electronic or hydraulic, should a problem occur.